Materials with good stretchability and elasticity are used to manufacture a variety of disposable articles in addition to durable articles including incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. For clothing, stretchability and elasticity are performance attributes that allow the materials to provide a closely conforming fit to the body of the wearer.
While numerous materials are known to exhibit excellent stress-strain properties and elasticity at room temperatures, it is often desirable for elastic materials to provide a conforming or secure fit during repeated use, during extensions and retractions at elevated or depressed temperatures, or in automobile interiors during summer months. Elasticity at elevated temperatures is also important for maintaining tight tolerances throughout temperature cycles. In particular, elastic materials used for repeated-wear clothing or garments must maintain their integrity and elastic performance after laundering.
Spandex™, a segmented polyurethane urea elastic material, is currently used in various durable fabrics. For example, fibers made from Spandex™ have been used in launderable apparels, fabrics, durable and disposable furnishing, beddings, etc. Similar to conventional uncrosslinked polyolefin-based elastic materials, articles made from Spandex™ can lose integrity, shape, and elastic properties when subjected to elevated temperatures. Thus, Spandex™ is not suitable for many co-knitting applications with high temperature fibers, such as polyester fibers.
Propylene-based polymers having good elastic properties are known and have been used for stretchable clothing. See, for example, U.S. Pat. Nos. 6,525,157 and 6,342,565. U.S. Pat. No. 6,342,565, in particular, discloses a soft, set-resistant, annealed fiber comprising a blend of polyolefins. The blend has a flexural modulus less than or equal to 12,000 psi and includes from 75 to 98 wt % of a first polymer component and from 2 to 25 wt % of a second polymer component. The first polymer component is a propylene-ethylene polymer having at least 80 wt % propylene and up to 20 wt % ethylene, a melting point by DSC in the range of from 25 to 70° C., and a heat of fusion less than 25 J/g. The second polymer component is a stereoregular isotactic polypropylene having a melting point by DSC of greater than 130° C., and a heat of fusion greater than 120 J/g. The fiber exhibits a resistance to set equal to or less than 80% from a 400% tensile deformation. The polyolefin blend is said to be substantially non-crosslinked.
U.S. Pat. No. 6,500,563 discloses blends of two different types of polypropylene, including blends made from a polypropylene having a Tm of less than 110° C. and propylene-ethylene copolymer that has isotactically arranged propylene derived sequences and Tm less than 105° C.
Three component blends of isotactic polypropylene, impact modifying amounts of an ethylene-propylene based rubber or low density ethylene copolymer and a propylene-based elastomer as compatibilizer are described in EP 946640, EP 946641, EP 969043 and EP 1098934.
WO 04/014988 describes blends of isotactic polypropylene with non-functionalized plasticizers such as poly-alpha-olefins. WO 03/040233 also discloses two component blends with the isotactic polypropylene as the predominant, matrix phase and the propylene-based copolymer serving as an impact modifier.
EP 1003814 and U.S. Pat. No. 6,642,316 disclose two-component blends of small amounts of isotactic polypropylene and predominant amounts of an ethylene based elastomer. EP 0374695 discloses visually homogeneous two component blends however using 40 wt % or less of the propylene-based copolymer. WO 00/69963 describes films made of two-component blends with from 75 to 98 wt % of a propylene ethylene based elastomer having a heat of fusion of less than 25 J/g.
Other related references include U.S. Publication Nos. 2006/102149; 2005/0107529; 2005/0107530; 2005/0131142; and 2005/0107534.
U.S. Pat. No. 7,867,433 discloses methods for making a crosslinked elastomeric composition and articles made therefrom. For example, an elastomeric composition comprising at least one propylene-based polymer is blended with at least one of multifunctional acrylates, multifunctional methacrylates, functionalized polybutadiene resins, functionalized cyanurate, and allyl isocyanurate; and blended with at least one of hindered phenols, phosphites, and hindered amines. The propylene-based polymer can include propylene derived units and one or more dienes, and have a triad tacticity of from 50% to 99% and a heat of fusion of less than 80 J/g. The blended composition can then be extruded and crosslinked. The extruded polymer can be crosslinked using electron beam radiation having an e-beam dose of about 100 KGy or less. The crosslinked polymers are described to be particularly useful for making fibers and films.
There is still a need for new and improved propylene-based materials requiring good stretchability and elasticity.